Q&A: Leaving Rigid Foam Exposed in Crawlspace

Q.I plan to install rigid foam
insulation in a crawlspace. As far as I know, most
types of rigid foam insulation can’t be left
exposed but need to be covered with a layer of drywall
for fire resistance. Is there a type of rigid foam
insulation panel available that can be left
exposed?

A.Corresponding editor Paul
Fisette responds: Not that I know of. However,
most building codes allow the installation of
unprotected rigid foam in a crawlspace that has no
open connection to a basement, as long as the foam
has passed alternative testing procedures. Dow
Styrofoam and Owens Corning Foamular are two
products that pass the burn test and can be left
unprotected in an isolated crawlspace.

Building codes restrict the use of unprotected
foam in habitable or accessible spaces. Different
code jurisdictions may have particular code
sections that deal with this issue. Some codes say
that if your crawlspace is connected to a basement,
you need to cover the foam with an ignition barrier
like 1/4-inch plywood or particleboard. Where
inspectors draw the line often depends on whether
there is a mechanical system in the crawlspace. The
thinking here is that a fire could be set off by
either the equipment or the activity of people in
the space. When in doubt, it always pays to talk to
your inspector during the design stage.